Drives for positioning actuators can have electronically commutated motors, for example. An electronically commutated motor, such as a synchronous motor, has a rotor with permanent magnets, which moves relative to a stator. The stator is provided with a plurality of stator coils, the energization of the stator coils in the correct rotor position generating a motor magnetic field which interacts with an excitation magnetic field generated by the permanent magnets in such a way that a desired drive force acts on the rotor. In order to achieve maximum efficiency, it is desirable that the motor magnetic field has a lead of 90° of an electric position angle in relation to the excitation magnetic field. For this reason, for the purpose of energizing the stator coils as a function of rotor position, information relating to the position of the rotor is needed. This rotor position can either be detected via sensors or determined by what are known as sensor-less methods for position detection.
By using the rotor position of the rotor and the desired direction of movement, an appropriate commutation pattern can be provided by a suitable control unit, said pattern determining how the stator coils are to be driven in order to provide the necessary drive force or the necessary torque.
In simple synchronous motors, the detection of the rotor position is carried out by an internal position sensor but there is also the possibility of arranging the position sensor externally on the actuator element or of additionally using a position sensor arranged there for the determination of the rotor position. As a result, the expenditure both for the synchronous motor and for the cabling between the synchronous motor and a control device can be reduced.
A synchronous motor can be driven with various types of commutation; in order to achieve the maximum drive moment, the motor magnetic field generated by the stator coils should if possible be set leading by 90° in the direction of movement in relation to the excitation magnetic field generated by the permanent magnets of the rotor. A deviation from this lead by 90° leads to a decrease in the drive force and the drive moment. In order to achieve driving always with the maximum possible torque, accurate rotor position information is necessary. Deviations between real and measured rotor position, which can be caused by sensor tolerances and resolution inaccuracies, for example, to some extent lead to considerable reductions in the efficiency.
In particular in an implementation of the positioning actuator with an external position sensor which picks up position information on an actuator element which is coupled by a step-down gearbox, the deviation between real and measured rotor position can be intensified further. One example in which an external position sensor can be provided is, for example, the throttle flap actuator, in which position feedback of the position of the throttle flap is present in any case in order to obtain accurate position information about the throttle flap. Use of the position information from the position sensor arranged on the throttle flap also for the commutation of the synchronous motor driving the throttle flap can lead to the aforementioned deviations and, as a result, to a considerable reduction in the actuating moment provided by the synchronous motor.
At very low temperatures, to which the motor system can be exposed, it is possible for icing to occur. This blocks the movement of the actuator element when operation of the motor system is resumed. In order to release this blocked state, in particular to carry out re-calibration of the rotor position by moving to a reference position or by moving to an end position, a maximum actuating moment from the synchronous motor is required immediately upon commencement of the starting process. In order to provide this maximum actuating moment, it is necessary for the deviation between real and measured rotor position to be as small as possible, so that the actuating moment can be as great as possible. On account of the temperature, however, a correspondingly pronounced temperature drift of the position sensor can lead to a significant error angle and therefore cause impermissible weakening of the torque of the synchronous motor. Under certain circumstances, the torque weakening can lead to it not being possible to release the iced actuator element from its blockage, and thus the motor system is not operational.
Furthermore, the position sensor on the actuator element is formed only as a relative position sensor, so that when activating the actuating system, the actual position of the rotor is not defined. While, for the purpose of calibration, the actuator element is normally moved to a predefined end stop, in order then to be able to drive the actuator element in an optimal way, this is not possible in the event of blockage of the actuator element, so that initial driving of the rotor with a maximum drive force is not possible.
The document DE 41 35 913 A1 discloses a method for controlling an adjusting device wherein, during the pre-starting phase and/or and after shutting down the drive unit or the vehicle, the adjusting device is moved at least once over the major part of its maximum possible movement range, starting from an arbitrary position for every possible direction of movement, so that, at least on one side, said adjusting device is led outside its normal operating movement range. In this way, jamming can be prevented.
The document DE 37 43 309 A1 discloses a method and a device for detecting a jammed or firmly frozen actuator element of an internal combustion engine, wherein the actuator element is shaken loose in the event of jamming. The shaking loose action can be carried out, for example, by the electric drive of the adjusting device being driven in a reversing manner.
The document DE 100 17 546 A1 discloses a method for detecting a blockage of the throttle flap on the basis of an actual value and a set point of the position of the throttle flap. Following the detection of a blockage, the set point for the position of the throttle flap is varied.
The document EP 0 391 930 B1 discloses a method for setting an operating characteristic of an internal combustion engine, wherein jamming of an actuator element for setting the air supply of the internal combustion engine is detected by using the deviation between predefined and instantaneous position and, if jamming is detected, the actuator element is caused to make a periodically shaking movement in order to release the jamming.
It is an object of the present disclosure to provide an improved method for releasing a blockage of an actuator element of a positioning actuator and/or for driving with a maximum actuating moment following activation of the motor system.